This thesis details the experimental development of a pneumatic infrasound generator, the purpose of which is for calibration, testing, and research. The source was an assembly of an air reservoir, a motor, and a rotor/stator pair, in the context of a siren. A rotating ball valve acted as the rotor/stator and modulated the compressed air from the reservoir as it vented into the atmosphere. The ball valve cross sectional area as a function of time varied as a triangular waveform, which in practice caused the infrasonic waveforms to be effectively sinusoidal. This thesis opens with a brief motivation for the creation of the source, in addition to previously developed infrasound generators and an overview of wind noise. The apparatus construction is then described. A theory is developed that describes the acoustic radiation from the infrasound generator as the superposition of a monopole and a dipole. Flow visualization, propagation, frequency response, reservoir volume, directivity, and jet velocity experimental setups and results are described next. The outcomes of the research are subsequently discussed, including a brief overview of a scaled up model of the infrasound generator. / text

Le coeur de cette thèse fait l'objet du traitement de signaux infrasonores et plus particulièrement de l'estimation et de la détection à l'aide d'un réseau de capteurs. Les thèmes abordés ici sont propices à l'expérimentation et nous avons essayé, autant que possible, d'illustrer les résultats théoriques obtenus à l'aide de données réelles. La première partie vise à décrire les implications et les difficultés liées à la détection de sources infrasonores. La littérature offrent déjà de nombreuses techniques de détection basées sur le test d'hypothèses qui sont alors exposées et complétées dans une optique de détection automatique. La seconde partie de cette thèse met en avant les erreurs de l'estimation de l'angle d'arrivée d'une onde lorsque les altitudes des capteurs d'une station sont ignorées (approximation courante). En réponse à ce problème, une estimation basée sur la géométrie complète de la station et comportant un a priori sur la vitesse de l'onde est dérivée et étudiée. L'estimation mentionnée ci-dessus permet de significativement améliorer les performances. Dans la troisième partie, nous introduisons la modélisation du signal infrasonore par un processus stationnaire de type autoregressif. Cette modélisation permet ensuite de développer une approche séquentielle pour la détection infrasonore basée sur le beamforming et la détection de hangement abrupte. La dernière partie de ce manuscrit a pour but de proposer un modèle "signal'' alternatif au modèle de retard pur. Il est présenté de nouveaux résultats mettant en avant un phénomène de perte de cohérence des signaux enregistrés par différents capteurs. Ces travaux aboutissent sur l'élaboration de méthodes de simulations de signaux synthétiques réalistes pour l'étude des performances des détecteurs infrasonores. / The core of this thesis is the infrasound signal processing and particularly the estimation and detection using a sensor array. The themes presented here are well-suited to experimentation and we tried, as much as possible, to illustrate the theoretical results with real data. The first part describes the implications and difficulties of infrasonic detection. We review the state-of-the-art of detection techniques based on hypothesis testing and supplement them with the aim of automatic detection. The second part of this thesis highlights the error on the angle of arrival estimation due to considering the arrays as planar (common approximation). In response to this problem, a new estimator considering the full geometry of the array and including an a priori on the speed of the infrasonic wave is derived and studied. We show that the described estimator significantly improve performance. The third part introduces the modeling of infrasonic signal as autoregressive process. This modeling allows us to derived a sequential approach to detect infrasound based on the beamforming and the detection of abrupt changes. The last part of this manuscript aims to propose an alternative "signal'' model. We present new results highlighting a phenomenon of loss of coherence of the signals recorded by different sensors. This work leads to the generation of synthetic infrasonic signal in order to study the performance of the detection algorithms.

Crocodilians (crocodiles, alligators, caimans and gharials) have a particular category of signals used for long-distance communication of location and status. These signals are composed of acoustic and non-acoustic components with different physical properties, such as vocal sounds, slaps, infrasound, odor and postures. A survey of extant species and a comparative study of allopatric conspecific populations inhabiting different habitats show that the composition of these signals is adjusted to optimize their ability to carry information in each habitat. Studies of animals living in changing habitats and of animals inhabiting different habitats within the same geographical areas show that these adaptations are evolved differences between populations and species rather than a result of behavioral adjustments by individual animals in response to habitat structure. Details of adjustment process help elucidate information about the functions of each signal component. Experimental data obtained in the course of the study show that crocodilians have the ability to locate the sound underwater. In addition, novel information on signaling by almost all extant crocodilian species is provided. This information gives important new evidence for solving the long-standing controversy of crocodilian systematic, showing that false gharials are aberrant crocodiles rather than members of the gharial lineage. It also sheds some light on the evolution of crocodilian signaling, allowing to plot the events of signal evolution on the phylogenetic tree, and explaining the puzzling absence of small species among extant crocodilians.

I recorded acoustic and visual components of Indian Peafowl (Pavo cristatus) mating displays at the Assiniboine Park Zoo, in Winnipeg, Manitoba, Canada. I determined that males produce infrasound (<20 Hz) in their train displays, and documented responses of peafowl to playbacks of both audible and infrasonic components of their vocalizations and train displays. Peafowl responded to infrasonic signals by increasing alertness and locomotory behaviours, while males also responded by calling. In response to audible call playbacks, males called and faced the playback unit while females increased locomotion and alertness, though peafowl did not respond to audible signal components from the train display, suggesting that infrasonic components constitute the essential signal component within those displays. Beyond revealing a critical role of acoustic signals in modulating interactions among peafowl, my results provide the first empirical evidence of a bird producing and perceiving infrasound as a signal.

I recorded acoustic and visual components of Indian Peafowl (Pavo cristatus) mating displays at the Assiniboine Park Zoo, in Winnipeg, Manitoba, Canada. I determined that males produce infrasound (<20 Hz) in their train displays, and documented responses of peafowl to playbacks of both audible and infrasonic components of their vocalizations and train displays. Peafowl responded to infrasonic signals by increasing alertness and locomotory behaviours, while males also responded by calling. In response to audible call playbacks, males called and faced the playback unit while females increased locomotion and alertness, though peafowl did not respond to audible signal components from the train display, suggesting that infrasonic components constitute the essential signal component within those displays. Beyond revealing a critical role of acoustic signals in modulating interactions among peafowl, my results provide the first empirical evidence of a bird producing and perceiving infrasound as a signal.

The Mississippi River Bridge in Vicksburg, MS is a 7 span cantilever bridge that is 3,389 feet long by 68.5 feet wide and is part of the Interstate-20 corridor. On March 23, 2011 at 1:30pm, a barge moving downstream struck a pier of the bridge. Infrasound stations located at the U.S. Army Engineer Research and Development Center (ERDC) detected the impact. Coincidentally, ERDC had instrumented the bridge with strain gages and accelerometers as part of a structural health monitoring project. Finite Element (FE) models were developed to investigate the structural behavior of the bridge due to the impact. The measurements and the FE models were used to determine the source mechanism of the infrasound from the bridge. Measurements from the sensors that were installed on the bridge will be presented along with FE models and infrasound data.

This thesis compares ash collected from different boilers cleaned using infrasound cleaning. The samples were evaluated from their physical properties, in an attempt to find connections between the difficulty to remove ash and its physical appearance. To get a deeper understanding of the mechanisms behind adhesion and fouling, and possibly explain results from the study of the ash samples, a literature review was carried out. The ash was also evaluated to see if any connections could be drawn between the physical properties of the ash and its fouling capabilities. A strong connection was found between ash density and its fouling capabilities. It was found that no dry ash with a density higher than 0.4 g/ml were difficult to remove with infrasound cleaning, and no ash with lower density was easy to remove. The ash density was calculated from a measurement of the weight of a certain volume of ash on a scale. Optical microscopy was used to study the ash samples, and gave an estimation of particle size, shape, and porosity. However, no clear connection could be observed with this method between the different samples and which were difficult to remove. The particle size for a few of the samples were also measured by a wet laser sieving method, and while it does give a good picture of particle size, the size was not found to be a useful prediction of the ash fouling behaviour. The exact mechanism giving rise to the density dependence need to be further investigated.

An abnormally high number of explosion quakes were noted during the monitoring effort for the 2007 eruption of Pavlof Volcano on the Alaskan Peninsula. In this study we manually counted the explosion quakes from their characteristic ground-coupled air waves. This study makes an effort at better quantifying the number of explosion quakes and how the characteristic ground-coupled air waves are affected by wind direction and wind speed. Additionally this study investigates how the ground coupled air waves might be used in a monitoring or analysis effort by calculating energy release and gas mass release. Over 3.2x104 quakes were recorded. It was found that wind direction affects the travel time of the air wave by up to 0.7 seconds depending on station location and wind direction. Wind direction and speed, however, are demonstrated not to cause an appreciable difference in ground-coupled air wave frequencies or amplitude ratios. The energy release from the explosions is calculated to be 3.04x1011 J. and the total gas mass (assuming 100% water) released was 729 metric tons. These values are compared to other volcanoes in the literature and found to be somewhat lower. Nevertheless, the tracking of explosion quakes has the potential to become a valuable member of the seismic monitoring arsenal.

As transportation infrastructure continues to age, new methods of non-contact monitoring should be evaluated and, if found suitable, employed for bridge monitoring and structural health assessment. This study highlights the use of infrasound monitoring, a geophysical technique utilizing acoustics below 20 Hz, as one possible solution for non-contact, non-line-of-sight infrastructure health monitoring. This dissertation focuses on the technique of infrasound for infrastructure monitoring (bridges are of primary interest) beginning with a literature review and an overview of current operational considerations for infrasound for infrastructure monitoring developed at the U.S. Army Engineer Research and Development Center. A meta-analysis of bridge vibrational characteristics was completed following identification of a gap in the knowledge base in this area. This completed meta-analysis compared vibrational characteristics across multiple bridge types and construction materials to determine applicability of infrasound for detection and monitoring of each bridge type. With these considerations in mind, an experimental series involving a steel, two-girder bridge in northern California was completed using infrasound to detect natural modes of the structure and validated by on-structure accelerometers. The non-contact nature of this structural assessment approach has potential to supplement traditional structural assessment techniques as affordable, remote, persistent monitoring of transportation infrastructure. Upon completion of the original experimental series, the data were used to investigate the possibility of wide area monitoring using infrasound, including possible limitations and boundaries. Overall implications for use of this technology are also discussed for a multiple infrastructure types.

With the aim of designing an infrasound-integrated technology which can enhance the algae drying performance, this thesis provided the theoretical possibility of using infrasound as an algae dehydration technology. To test the relation between algae drying speed and other three parameters namely sound frequency, sound pressure and sample mass, four major experimental groups including initial experiments and core experiments with fifteen sub-experimental groups are designed. Results of the experiments shows expected accordance with the theoretical inferences of infrasound being an algae drying technology. Experiment steps and specifications are presented as the research methodology. A real system with the drying capacity of 2 ton fresh algae per day are designed based on the experimental calculations and results. Several revisions including air circulation and infrasound resonance are made when scaling up the research from experimental level up to industrial level. Other specifications of the real system design follow the experiment results with regard of the research consistency. Freeze drying technology is selected for the comparative cost analysis including manufacturing costs and energy consumptions. Results shows infrasound-integrated technology has a relatively low energy consumption whereas it costs more manufacturing costs than freeze drying technology. Research assumptions, limitations and recommendations for this research are described in this article. From the author’s perspective, this paper can be used as an initiation and instruction for larger scale researches in regard of infrasound-integrated algae dehydration/drying.